The present invention relates to a heating and extruding method and device for a bulk preform formed of a thermosetting or thermoplastic synthetic resin material in which reinforcing fibers are uniformly dispersed.
A composite material composed of a thermosetting or thermoplastic synthetic resin and reinforcing fibers uniformly dispersed in the synthetic resin has excellent characteristics (especially, tensile strength and impact strength), and so the composite material is widely used as various materials for a panel, shell, body, container, etc. according to a thermal characteristic of the synthetic resin. Such a composite material is handled as a preform in the form of a sheet or a bulk or block before being finally formed into a molded part having a desired shape. In the course of obtaining the molded part from the preform, the preform is heated by any method according to the kind of the synthetic resin and the shape of the preform.
Conventionally, a sheet-like preform is generally used for the reason why it can be easily uniformly heated and it is superior in postformability upon compression molding into a molded part having a desired shape. A molding system using such a sheet-like preform is shown in FIG. 5. Referring to FIG. 5, a plurality of sheet-like preforms 3 are heated in a heating machine 1 such as an infrared heating oven before they are successively supplied into between an upper mold 5a and a lower mold 5b of a compression molding machine 2. That is, a resin sheet is previously cut into the sheet-like preforms 3 each having a suitable size according to a shape of a molded part, and the sheet-like preforms 3 are put on a conveyor 4 to be subjected to uniform heating in the heating machine 1. The sheet-like preforms 3 thus heated are stacked on the lower mold 5b according to a desired thickness of the molded part, and both the upper and lower molds 5a and 5b are approached each other to obtain the molded part having a desired thickness.
However, since the sheet-like preforms are heated in the atmospheric air, the resin material composing the sheet-like preforms is oxidized and degraded to often cause a reduction in quality of the molded part. Further, a part of the resin material is decomposed to liable to generate soot because of atmospheric heating, resulting in blackening of the molded part.
On the other hand, when using such sheet-like preforms, it is necessary to previously cut an elongated sheet into a plurality of sheet-like preforms and set them on the mold. Further, in the case where the molded part is thick, it is necessary to stack the sheet-like preforms on the mold. Thus, the sheet-like preforms heated to high temperatures must be handled to render the working troublesome and accompany danger. In addition, it is difficult to automate the step of supplying the heated sheet-like preforms to the compression molding machine.
Further, the use of the sheet-like preforms causes the following problems, and so the demand for use of bulk preforms has recently been increased.
(1) A manufacturing method for the sheet-like preforms is complicated to increase a manufacturing cost. PA1 (2) The reinforcing fibers in the composite material are often broken in a kneading or preforming step, thus reducing a strength of the molded part. PA1 (3) Before molding the sheet-like preforms, the resin sheet must be cut in consideration of a desired size of the molded part, and the sheet-like preforms must be often stacked on the mold in consideration of a desired shape and thickness of the molded part, thus reducing a molding efficiency and increasing a molding cost.
On the other hand, there has been disclosed in Japanese Patent Laid-open Publication No. 1-210315, for example, a technique of heating and metering a bulk preform before molding. That is, as shown in FIG. 6, an extruding machine 102 is used to quantitatively supply a melted composite to a compression molding machine 105.
More specifically, a heating machine 101 for heating a bulk preform A1 is connected to the extruding machine 102. A pressure cylinder 119 is provided at one end of a cylindrical extruding container 102a of the extruding machine 102, and an extruding lip 103 is provided at the other end of the container 102a. A bulk preform A2 heated is pressurized in the container 102a by the pressure cylinder 119, and is discharged as a melted composite A3 from an opening 107 of the extruding lip 103. The melted composite discharged in a predetermined amount is cut by a cutter 104 provided at the opening 107, and a melted composite A4 thus obtained is supplied to between an upper mold 106a and a lower mold 106b of the compression molding machine 105.
In cutting the melted composite discharged from the opening 107 of the extruding lip 103, an extrusion length of the melted composite is changed to be decided according to a weight of the molded part. However, an extrusion thickness and an extrusion width of the melted composite are not adjusted according to a desired shape of the molded part, but they are fixed. In other words, a shape (especially, a thickness and a width) of the melted composite is not always be suited to the desired shape of the molded part. Accordingly, spreading distances in a longitudinal direction and a lateral direction of the melted composite upon compressed by the upper and lower molds 106a and 106b are often unbalanced to cause orientation of reinforcing fibers in the molded part and therefore enlarge an anisotropy in strength of the molded part.